It’s February, and the seed catalogs are here. Actually, they’ve been rolling in since last fall, tantalizing gardeners with gorgeous pictures of heirloom flowers and vegetables. But as tempting as it is to go ahead and start our seeds a little early, starting seeds too soon has disastrous consequences.

Seeds started too early tend to produce weak, spindly seedlings that won’t survive the stress of transplanting. Have a little patience, do the necessary research, and use tools like a cold frame or greenhouse to start seedlings reasonably early for a healthy, productive garden. 

What happens if I start seeds too early?

While starting seeds early seems like a good way to get ahead of the gardening season, starting seeds too early causes far more problems than it cures. 

1. Leggy seedlings

In temperate climates in the northern hemisphere, daylight hours vary during the year. This means that there is less natural light in midwinter than there will be in late winter and early spring when the days are longer.

Seedlings will reach for indirect, low light if that is their only option. As a result, the seedlings become leggy, with weak stems and roots since they lack sufficient light and nutrients.

2. Rootbound seedlings

You can work around the natural lighting issue by using a grow light on seedlings, but this sometimes causes another problem. Seedlings that mature too fast may become rootbound and need to be transplanted into bigger pots. 

Potting up seedlings can get expensive, as you may need to buy more pots and potting soil. Bigger pots also take longer to water and are more difficult to move–ultimately making more work for you. 

3. Transplant shock

The other problem with starting seeds too early is that the plants mature in their pots, rather than in the garden. It may feel like you’re getting a headstart on the season to see your plants flowering and beginning to make fruit, but the truth is that plants at this stage are so far along in their life cycles that they will struggle when they are finally transplanted outside. 

Young seedlings have the best chance of surviving transplant shock because all of their energy is being put towards developing a healthy root system. Older plants have surpassed this point and are much more concerned with setting seed–making these plants less likely to survive the transition. 

4. Premature bolting

Stressed plants that were started too early are more apt to bolt than plants that are at the correct stage of development. Seedlings that have been in pots too long won’t be as productive and will bolt far sooner than seedlings that have the time and space to mature normally.  

5. Weakened immunity

Weakened immunity isn’t tied directly to an early seed sowing date, but weak, leggy seedlings are more likely to succumb to diseases like damping off than seedlings that never became stressed in the first place.

Diseases and pests pressure are often unavoidable, but healthy seedlings are more likely to survive infestations and damage than seedlings weakened by cold temperatures and insufficient light. 

How early can I start seeds indoors?

There is no universal rule for when to start your seeds. Plants mature at different times and require different temperatures to germinate. Your best bet is to refer to the seed packet for the ideal planting window. 

If you aren’t sure what hardiness zone you grow in, reference this USDA map. The map itself only portrays hardiness zones in the United States, but the map legend lists the average lowest temperature and average highest temperature for each zone, in both Fahrenheit and Celcius. If your country doesn’t already have a hardiness zone map, the USDA map legend can help you determine which planting zone your growing region is in. 

If you live in the United States, use The Almanac’s planting calendar to determine a general time frame for when to start specific crops. The Almanac’s planting calendar has the added benefit of listing the average last spring frost and the average first frost for your growing zone.

The best way to decide when to sow seeds is by picking a goal date to transplant seedlings outside–bearing in mind that this date needs to account for spring frosts in your hardiness zone. Take that date and count backward X number of weeks, depending on the weeks to maturity listed on the seed packet for that specific crop.

Which seeds can I start early?

Cool-season crops like brassicas, peas, and lettuces can usually go in the ground before the last spring frost. In temperate climates, start cool-season brassicas in March, and don’t be afraid to transplant out in April. Direct sow pea seeds as soon as the soil is workable.

Heat-lovers like tomatoes, peppers, beans, and squash prefer to be direct-seeded after all danger of frost has passed–well into May in temperate regions. Some warm-season crops like tomatoes and peppers benefit from being sown up to eight weeks before the last spring frost, especially those varieties that take longer to mature. 

Rutgers University has created a reference table that identifies common vegetables as either warm-season or cool-season vegetables. One column in the table lists the number of weeks from seeding to transplanting.

Can seeds sprout too quickly?

If your seeds germinated much faster than you anticipated, pat yourself on the back–you’re doing something right. While most seeds take a week or two to germinate, if you provide seeds with ideal temperatures, moisture, and humidity, you may see some seedlings pop up in as little as three days!

What happens if I transplant seedlings too early? 

Seedlings that go outside before they’ve been properly hardened off will undergo some stress, but it’s nothing that they can’t bounce back from! Seedlings show signs of transplant shock in the form of yellowing leaves, wilting, and possibly dying off

Remedy transplant shock by using some of the tools identified below. For more information on transplant stress and how to prevent it, view my article on transplant shock here

5 tools to start seeds early

With the proper tools and equipment, some crops may be started well before the last spring frost.

1. Cold frames

Cold frames are growing boxes with a lid. Most cold frames are made out of wood planks and have a glass window or door for a lid, but you can get creative if you’re building your own! 

Cold frames extend the season from one to three months. An excellent investment for your garden, cold frames can be used to harden off seedlings or to grow cool-season crops like lettuce and brassicas.

Either line the bottom of your cold frame with gravel to rest seedlings trays on top of, or fill the box with potting soil to grow starts directly in. You might even consider storing your root vegetable harvest in a cold frame come fall! 

2. Floating row cover 

Floating row cover has saved many a crop in the garden. We think we’re past all danger of spring frost, but lo and behold, winter hangs on until the bitter end. 

If you transplanted your warm-season seedlings a little too soon, all hope is not lost. Simply install a few wire hoops over the rows or raised beds and drape floating row cover over top. Make sure that the fabric doesn’t actually touch the seedlings, and the air pocket created will raise the temperature under the fabric by at least 5 degrees. 

3. Greenhouses

Greenhouses are a luxury that not all gardeners have access to. If you do have access to one, rejoice! You can start your seeds about two months early with few consequences. 

If you don’t have a greenhouse, you can still run a legit seed-starting operation in your home, or heated garage or shed. Investing in heat mats and grow lights will make for healthy seedlings and less stress on your end.

4. Heat mats

Heat mats are nifty tools that work to raise the soil temperature to a degree that suits your seedlings. Generally made out of rubber and waterproof, heat mats are an excellent tool to jumpstart germination. 

Different seedlings require different temperatures to achieve ideal germination. Check out this study from the University of California on the effects of soil temperature on vegetable seed germination.

5. Grow lights

Grow lights aren’t essential to your seed-starting setup, but they are an incredibly useful tool. Sometimes a west or south-facing window will do the trick, but placing seed trays near a window will sometimes result in spindly seedlings that stretch for the light. 

Grow lights come in a variety of sizes, styles, and prices–pick one that fits your needs and budget. White LED lights are fine for seed starting, but you’ll need a full-spectrum light once your seedlings begin to grow. 

I’ve had amazing success with my setup of TSL 2000W lights from Mars Hydro last year – the only one thing to keep in mind is that seedlings grow extremely fast under them.

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While it’s so tempting to start sowing seeds in midwinter, it’s not in your (or your garden’s) best interest. Gardening is all about timing, and the time it takes for a seed to mature is really out of our control. So, busy yourself with other garden tasks during the bleak midwinter and invest in a few pieces of equipment that will allow you to extend your season reasonably. 

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